There is an ongoing need for acoustic wave filters and delay lines for a variety of practical applications. Acoustic wave devices are becoming particularly important in the production of electronic signal processing equipment, especially radios, because they can be readily mass produced and are of small size. Acoustic wave devices are generally constructed on planar surfaces using integrated circuit fabrication techniques.
A number of low-loss acoustic wave filter and transducer design approaches have been developed to meet specific performance goals relevant to particular applications and subject to specified manufacturing constraints. These approaches include multiphase unidirectional acoustic wave transducers, multi-transducer acoustic wave filters, resonators, distributed acoustic reflection transducers (DARTs) and acoustic wave transducers backed by reflectors, with each acoustic device type providing filter performance strengths and weaknesses.
Examples of these and other types of acoustic wave devices are described in U.S. Pat. No. 4,602,228, entitled "Surface acoustic wave filter", by J. Yamada; U.S. Pat. No. 4,492,940, entitled "Acoustic surface wave bandpass filter", by M. Hikita; U.S. Pat. No. 4,760,359, entitled "Surface acoustic wave resonator", by T. Shiba et al.; U.S. Pat. No. 4,837,476, entitled "Surface acoustic wave resonator having transducers and reflectors of different periods", by M. Mochizuki; U.S. Pat. No. 4,742,319, entitled "Surface-acoustic-wave resonator", by T. Sone; U.S. Pat. No. 4,249,146, entitled "Surface acoustic wave resonators utilizing harmonic frequencies", by K. Yen et al.; U.S. Pat. No. 4,162,465, entitled "Surface acoustic wave device with reflection suppression", by B. J. Hunsinger and K. Hanma; and U.S. Pat. No. 4,642,506, entitled "Surface acoustic wave device with reflectors in inter-electrode location", by M. F. Lewis, which are incorporated herein by reference. However, these and other prior art approaches suffer from a number of disadvantages well known in the art. These disadvantages tend to become more serious as operating frequency increases.